1.0 Field of the Invention
The present invention relates generally to gas turbine engines, and more particularly, to a system for supplying extracted, cooled, compressed/intercooled, cooling and combustion air for gas turbine engines.
2.0 Related Art
The highest temperatures in gas turbine engines are typically found in the combustor and the turbines. The continuing demand for larger and more efficient gas turbine engines creates a requirement for increased turbine operating temperatures. However, as the combustor and turbine hot gas temperatures have been increased to achieve increased output and thermal efficiencies, the challenge to maintain component lives, due to the metallurgical limitations of critical hot components such as the turbine rotor blades and disks, as well as the challenge to control NOx emission levels has also increased.
Conventional air-cooled gas turbine engines typically extract cooling air from one or more stages of the high pressure compressor to provide cooling for elements of the combustor and high pressure turbine. Among the more recent of the known systems for providing cooling air to critical hot section components are those shown in U.S. Pat. Nos. 5,305,616 and 5,392,614, each issued to Coffinberry and assigned to the assignee of the present invention, each of which is expressly incorporated by reference herein in its entirety. Each of the various embodiments disclosed in the Coffinberry patents utilizes a first stream of cooling air extracted from the discharge of the high pressure compressor which is further compressed using a turbocompressor and cooled in a heat exchanger prior to cooling elements of the high pressure turbine and combustor. The turbine section of the turbocompressor is driven by air extracted from a mid-stage of the high pressure compressor. Other known systems utilizing a turbocompressor to further compress and cool extracted air from a high pressure compressor of a gas turbine engine have included a heat exchanger disposed between the compressor and turbine sections of the turbocompressor such that the inlet to the heat exchanger is in fluid flow communication with the outlet of the compressor section and the outlet of the heat exchanger is in fluid flow communication with the inlet of the turbine section. While such systems advantageously provide cooling air having a higher pressure and cooler temperature then would otherwise be available to hot section components, such systems are subject to the following disadvantages. Compressor discharge air is relatively expensive air, in terms of engine performance, and additionally is relatively difficult to further compress as compared to a lower pressure source of cooling air. Accordingly, gas turbine engine designers continue to search for new and improved cooling air systems, with issues including system pressure drop, compression power requirements, heat exchanger costs and reliability, and equipment size and weight, etc.